Numerous apparatus requires the dispensing of sheet material from a roll to the apparatus. In many instances, notably wrapping machines, such as plastic film wrappers and the like, the wrapping sheet material is dispensed intermittently to the wrapping apparatus as a package advances therethrough, with no sheet material being dispensed to the apparatus during the sealing of the package and during the reverse stroke of the apparatus.
Rolls of sheet material, such as plastic film, paper, aluminum foil and the like, are quite heavy. Thus, the removal of sheet material from these rolls begins the rotation of a large mass, with the roll tending to maintain its rotation by its own momentum, leading to a loss of tension in the dispensing apparatus. For this reason, many intermittent sheet dispensing mechanisms do not permit the roll of sheet material to be dispensed under low tensions. Alternatively, the rolls of sheet material are mounted on a motor driven support, such that the roll can be rotated when positively driven. While motor driven sheet dispensing mechanisms permit low tension feeding, these motor driven unwinders are expensive and require electrical and mechanical maintenance.
It is thus a primary object of the present invention to provide an apparatus for dispensing sheet material from a roll in which low tension control of the sheet material can be maintained while intermittently dispensing sheet material without the necessity of a motor driven unwind.
Another problem common to apparatus employing intermittent sheet material dispensing, and notably wrapping machines, is that the end of the sheet material which is cut from the package as it is sealed is free, i.e., is not held in place by any means. Thus, when any tension is maintained in the dispensing apparatus for the sheet material to be dispensed to the apparatus using this sheet material, pull back of the free end of the sheet material into the dispensing apparatus can be a problem.
It is thus another primary object of the present invention to provide a sheet material dispensing apparatus which eliminates pull back of the free end of sheet material.
Still another problem when dispensing from rolls of sheet material is the reduction of inertia as the mass of the roll decreases, thus causing changes in tension in the sheet material within the dispensing apparatus.
It is thus another object of the present invention to eliminate the effect in inertial force changes of the roll.